J. Am. Chem. SOC.1992, 114, 1729-1732
product yields, etc.). The same is equally true of the work described in this paper. Although TRIR has played a key role in unravelling the mechanism of these reactions, the results of many other experiments including the flash photolysis4of [CpFe(CO),],, the characterization of C P , F ~ ~ ( C Oin) ~low-temperature matrice^,^,^ and measurements of quantum yields21,22bhave been important in constructing the complete mechanism shown in the schemes. The great strength of TRIR, however, is that the narrow line width of u(C-0) bands allows one to monitor each intermediate in real time in the reaction mixture, thus reducing the need to speculate when devising the overall mechanism for a reaction. TRIR has now been applied to the reactions of a number of related dinuclear complexes,53and we are currently extending this work to establish whether the behavior of [ C P F ~ ( C O )is~ ] ~ typical of such compounds.
Acknowledgment. We thank SERC, the EC Science Program (Contract ST0007), NATO (Grant No. 900544), the Petroleum Research Fund, administered by the American Chemical Society,
1729
the Paul Instrument Fund of the Royal Society, Miitek GmbH, Perkin-Elmer Ltd., and BP International Ltd for their financial support. We are grateful to Dr. S. Firth, Dr. S.A. Gravelle, Dr. M. A. Healy, Dr. P. M. Hodges, Dr. S. M. Howdle, Ms. M. Jobling, Mr. F. P. Johnson, Dr. B. D. Moore, Professor R. N . Perutz, Professor N . Sheppard, Dr. L. J. Van der Burgt, and Dr. A. H. Wright for their help and advice. We thank Professor E. Weitz, Professor J. M. Kelly, and Dr. C. Long for access to equipment in their laboratories. Finally, we thank Mr. D. R. Dye, Mr. J. G. Gamble, Mr. D. Lichfield, Mr. R. Parsons, Mr. W. E. Porter, and Mr. J. M. Whalley for their continued assistance in developing and building the TRIR equipment at Nottingham. Registry No. 3, 87985-70-4; [CpFe(CO),],, 12154-95-9; CpFe(C0)2, 55009-40-0; Cp2Fe(CO),(THF), 138489-71-1; CpFe(CO)P(OMe),, 1 13843-93-9; CpFe(CO)PO'Pr),, 138489-74-4; CpFe(CO)P(OEt)3, 138489-75-5; CpzFq(CO),P(OMe)3,33087-08-0; Cp2Fe2(CO),P(OEt),, 33057-34-0; Cp2Fe2(CO)3P(FPr)3, 33218-96-1; [CpFe(CO)P(OMe),],, 71579-40-3; [CpFe(CO)P(OPr),],, 138489-72-2; [CpFe(CO)P(OEt),],, 138489-73-3.
Polymorphism of 1,3-Phenylene Bis( diselenadiazolyl). Solid-state Structural and Electronic Properties of A. W. Cordes,*J*R. C . H a d d o n , * , l b R. G. Hicks,Ic R. T. Oakley,*Jc T. T. M. P a l s t r a , l b L. F. Schneemeyer,Iband J. V. WaszczakIb Contribution from the Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas 72701, AT& T Bell Laboratories, Murray Hill, New Jersey 07974, and Guelph Waterloo Centre for Graduate Work in Chemistry, Guelph Campus, Department of Chemistry and Biochemistry, University of Guelph, Guelph, Ontario N l G 2W1, Canada. Received August 12, 1991
Abstract: The solid-state characterization of a second or @-phaseof the 1,3-phenylene-bridged diselenadiazolyl diradical 1,3-[(Se2N2C)C6H4(CN2Se2)] is reported. Crystals of this @-phaseare monoclinic, space group P 2 , / n , with a = 9.108 (6), b = 15.233 (13), c = 16.110 (5) A, @ = 103.37 (S)', Z = 8. The crystal structure consists of chain-like arrays of discrete dimers (4 per unit cell), although one intradimer S e s e linkage is notably longer (3.411 A) than the other three (3.125, 3.196, 3.204 A). The dimer units lie in chains that are linked by a complex three-dimensional array of Se-Se contacts. Variable-temperature single-crystal conductivity measurements on this phase indicate a band gap of 0.77 eV. Consistent with the conductivity measurements, extended Hiickel band structure calculations suggest a relatively isotropic electronic structure.
Introduction Our interest2 in the construction of molecular conductors from neutral *-radicals has prompted us to investigate the use of thiazyl and selenazyl radicals as molecular building blocks. Of the various radical derivatives that have been e x p l ~ r e d ,those ~ . ~ based on the (1) (a) University of Arkansas. (b) AT&T Bell Laboratories. (c) University of Guelph. (2) (a) Haddon, R. C. Nature (London) 1975, 256, 394. (b) Haddon, R. C. Aust. J. Chem. 1975, 28, 2343. (3) (a) Wolmershiuser, G.; Schnauber, M.; Wilhelm, T. J. Chem. SOC., Chem. Commun. 1984, 573. (b) Wolmershiuser, G.; Schnauber, M.; Wilhelm, T.; Sutcliffe, L. H. Synth. Met. 1986, 14, 239. (c) Dormann, E.; Nowak, M. J.; Williams, K. A,; Angus, R. 0.. Jr.; Wudl, F. J. Am. Chem. Soc. 1987, 109, 2594. (d) Wolmershiuser, G.; Wortmann, G.; Schnauber, M. J. Chem. Res. Synop. 1988, 358. ( e ) Wolmershauser, G.; Johann, R. Angew. Chem., Int. Ed. Engl. 1989, 28, 920. (f') Hayes, P. J.; Oakley, R. T.; Cordes, A. W.; Pennington, W. T. J. Am. Chem. SOC.1985,107, 1346. (9) BoerE, R. T.; Cordes, A. W.; Hayes, P. J.; Oakley, R. T.; Reed, R. W. Inorg. Chem. 1986,25,2445. (h) Oakley, R. T.; Reed, R. W.; Cordes, A. W.; Craig, S. L.; Graham, J. B. 1987, 109, 7745. (i) BoerE, R. T.; French, C. L.; Oakley, R. T.; Cordes, A. W.; Privett, J. A. J.; Craig, S. L.; Graham, J. B. J. Am. Chem. Soc. 1985,107,7710. (j) Awere, E. G.; Burford, N.; Haddon, R. C.; Parsons, S.;Passmore, J.; Waszczak, J. V.; White, P. S. Inorg. Chem. 1990, 29, 4821. (k) Banister, A. J.; Rawson, J. M.; Clegg, W.; Birkby, S. L. J. Chem. SOC.,Dalton Trans. 1991, 1099.
1,2,3,5-dithia- and 1,2,3,5-diselenadiazolylring systems are particularly appealing as precursors for new materialsS5s6Toward this end we recently described the preparation and solid-state structural and electronic properties of the 1,3- and 1,4phenylene-bridged bis(dithiadiazoly1) and bis(diselenadiazoly1) diradicals [(E2N2C)C6H6(CN2E2)] 1' and 2' (E = s,Se). In the (4) Cordes, A. W.; Haddon, R. C.; Oakley, R. T. In The Chemistry of Inorganic Ring Systems; Steudel, R., Ed.; Elsevier: Amsterdam, 1992. (5) Vegas, A.; Perez-Salazar,A.; Banister, A. J.; Hey, R. G. J . Chem. Soc., Dalton Trans. 1980, 1812. (b) Hofs, H.-U.; Bats, J. W.; Gleiter, R.; Hartmann, G.; Mews, R.; Eckert-MaksiE, M.; Oberhammer, H.; Sheldrick, G. M. Chem. Ber. 1985, 118, 3781. (c) Fairhurst, S. A.; Johnson, K. M.; Sutcliffe, L. H.; Preston, K. F.; Banister, A. J.; Hauptmann, Z. V.; Passmore, J. J . Chem. Soc.,Dalton Tram. 1986, 1465. (d) BoerE, R. T.; Oakley, R. T.; Reed, R. W.; Westwood, N. P. C. J. Am. Chem. Soc. 1989,111, 1180. (e) Banister, A. J.; Hansford, M. I.; Hauptmann, Z. V.; Wait, S. T.; Clegg, W. J. Chem. SOC.,Dalton Trans. 1989, 1705. (0 Cordes, A. W.; Goddard, J. D.; Oakley, R. T.; Westwood, N. P. C. J. Am. Chem. SOC.1989, 111,6147. (6) Del Bel Belluz, P.; Cordes, A. W.; Kristof, E. M.; Kristof, P. V.; Liblong, S. W.; Oakley, R. T. J. Am. Chem. SOC.1989, 111, 9276. (7) Andrews, M. P.; Cordes, A. W.; Douglass, D. C.; Fleming, R. M.; Glarum, S. H.; Haddon, R. C.; Marsh, P.; Oakley, R. T.; Palstra, T. T. M.; Schneemeyer, L. F.; Trucks, G. W.; Tycko, R.; Waszczak, J. V.; Young, K. M.; Zimmerman, N. M. J. Am. Chem. SOC.1991, 113, 3559.
0002-7863/92/1514-1729$03.00/00 1992 American Chemical Society
Table I. Unit Cell Parameters for a-and B-Phases of I (E = Se) and
Selected Structural Data (Distances in A) ~~
spa=
phase group a
14,/a
8
P2l/n
b
a
34.617 (13) 9.108 (6)
8
C
1 1 Cordes et al.
1730 J. Am. Chem. Soc.. Vol. 114, No. 5, 1992
7.228 (4) 15.233 (13) 16.1 10 ( 5 ) 103.37 (5)
SE2
SW
c4
Selected Distances in @-Phase Sel-Se2 Se5-Se6
Se 1 -Se7 Se3-Se5 dl (Se2-Se8') d2 (Se3-Se3') d , (SebSe8')
2.345 (3) 2.344 (3) 3.204 (3) 3.125 (3) 3.859 (3) 3.979 (3) 3.779 (3)
2.321 (3) 2.335 (3) 3.196 (3) 3.411 (3) 3.865 (3) 3.816 (3)
Se3-Se4 Se7-Se8 Se2-Se8 Se4-Se6 d, (Se6-Se7') ds (Se7-Se8')
N7
solid state the former stack in a vertical fashion with individual "plates" linked by a zigzag network of E-E contacts, Le., 3. The latter stack as interleaved arrays of diradical dimers, Le., 4.
1
3
SE7
N5
SM
SU
Figure 1. A single dimer unit in the @-phaseof 1 (E = Se), with atom numbering.
z
4
During our work on the physical characterization of these species we have discovered that the 1,3-selenium derivative 1 (E = Se) can also be generated in a second or 8-phase. Herein we report the structural characterization of this new phase and compare its magnetic and conductivity properties with those of the previously described a-phase 3. The results are discussed in the light of extended Hiickel band structure calculations.
Figure 2. A schematic view of the chain-like arrangement of dimers in the yz plane. Shaded molecules lie slightly below and unshadcd molecules slightly above the plane of the paper. Short interdimer S t S e contacts (as defined in Figure 4 and Table I) are shown as dashed lines.
Results and Discussion Crystal Structure. Golden blocks of @- 1,3- [(SqN2C)C6H4(CN,Se,)] are monoclinic, space group P2,/n. Unit cell parameters for this second phase (as well as those of the a-phase) are summarized in Table I, along with selected internuclear distance information. In the @-phasethe diradicals associate into dimeric units, with four dimers to the unit cell. An ORTEP drawing of a single dimer unit is shown in Figure 1. The internal structural parameters of the dimers are similar to those seen in other diselenadiamlyl structures.68 There is, however, one unusual feature regarding the intradimer &Se contacts; while Sel-Se7, Se2-Se8, and Se3-95 are similar to those Seen before, the W-Se6 linkage is significantly longer. There is no indication of the kind of molecular stacking found in either the a-phase or the 1,4-derivative 4. Instead the crescent-shaped dimers coil together to produce chain-like arrays
Figure 3. A local view of the packing in the yz plane and definition of the contacts d,-d,.
(8) Cordes, A. W.; Haddon, R. C.; Oakley, R. T.; Schneemeyer, L. F.; Wastnak, J. V.; Young, K. M.; Zimmerman, N. M. J. Am. Chem. Sm. 1991, 113. 582.
parallel to the z axis (seeFigure 2). The molecular packing gives rise to a complex three-dimensional network of close interdimer Se-Se contacts. Within the chains every diradical dimer has two
z
Y-
Polymorphism of 1,3-Phenylene Bis(diselenadiaroly1)
J. Am. Chem. SOC.,Vol. 114, No. 5, 1992
1731
TEMPERATURE ( K )
500
400
300
200
I
I
I
1
D-PHASE
TEMPERATURE ( K )
Figure 4. Magnetic susceptibility of the &phase of 1 (E = Se) as a function of temperature. 3
2
Table 11. Magnetic and Conductivity Parameters for the a- and &Phases of 1 (E = Se)
phase concn of defects (% per molecule)
e (K)
B
a’ 0.51 -1 -164
diamagnetism (ppm emu mol-’) band gap (eV) 0.55 carrier density (per molecule, at 300 K) 1.3 X 10” mobility (cm2 V-I s-], at 300 K) 2.2 “From ref 7.
5
4 lOOO/T K”
Figure 5. Log plot of single-crystal conductivities of a-and &phases of 1 (E = Se) as a function of inverse temperature.
1.31 1 -219
0.77 1.8 X 150
nearest neighbors, one based on a convex and the other a concave approach of two dimers; each of these arrangements straddles a crystallographic inversion center. The close Se-Se contacts d , , d,, and d5 arising from these approaches, illustrated schematically in Figure 3 and crystallographically in Figure 3, provide the ‘‘links’’ along the chains. It should be noted that dl and d5 are not to the same dimer unit; the former is between Se8’ and Se2 in a radical unit above it, while the latter is from Se8’ to Se7 in a radical beneath it. The third type of interdimer contact, characterized by the distances d3 and d4, represents the approach of one dimer to the underside of another. Both of these contacts, which are reminiscent of the butt-end contacts observed in the 1,Cstructures 4, involve the same atom (Se6) with the longest intradimer bond (3.411 A). These final contacts provide a mechanism for orbital interactions between adjacent molecular chains. Magnetic Susceptibility and Conductivity Measurements. The measured magnetic susceptibility of the @-phaseof 1 (E = Se) as a function of temperature is shown in Figure 4. The lowtemperature susceptibility shows Curie behavior, due to a small concentration of defects, which are associated with unpaired electrons. The concentration of paramagnetic defects, along with the 0 value and measured diamagnetism for both the a- and @phases, are given in Table 11. Log plots of the single-crystal conductivity of the two phases are shown in Figure 5 . If, as before,’ we treat the material as an intrinsic semiconductor, we obtain the conductivity parameters listed in Table 11. In contrast to the needle-like appearance of the a-phase, the morphology of the @-phaseallowed us to use the van der Pauw technique for conductivity measurements; these indicated that the conductivity of the latter phase is isotropic in the two dimensions examined. The conductivity behavior of the two phases is rather similar. The higher mobility of the @-phasemay be a reflection of the isotropic nature of this phase. Band StructureCalculatiorrs. Three-dimensional band structure calculations were performed using extended Huckel methods with a parameterization scheme described previously.* As illustrated by the density of states curves shown in Figure 6, and in accord with the conductivity measurements, there is a substantial band gap at the Fermi level for @phase. The calculated band gap of 1.2 eV is larger than that predicted for the a-phase (0.8 eV). The &phase is, however, more isotropic than the a-phase. Summary and Conclusiom. In our search for neutral molecular materials which possess the desirable structural, thermal and electronic properties for electronic conduction we have explored
ENERGY( eV )
a-PHASE
-5
I
,
1
,
I
I
I
,
,
I
,
I
,
J. Am. Chem. SOC.1992,114, 1732-1735
1732
of needles of the a-phase and blocks of the new 8-phase is produced; the two phases can be separated manually. The a-phase is more volatile; it can be resublimed under less extreme conditions and tends to vaporize from a heated finger more readily than the &phase: dec (@-phase)>350 O C ; infrared spectrum (8-phase, 1600-250 cm-I region) 1331 (m), 1307 (s), 1281 (m), 1255 (w), 1247 (w), 1142 (m), 1079 (w), 1068 (w), 919 (w), 805 (w), 796 (w), 750 (m), 733 (m), 688 (vs), 678 (vs), 649 (m), 616 (s), 391 (s) cm-l. X-rayMeasurements. A brass-colored block of the &phase of 1 was mounted on a glass fiber and coated with epoxy. X-ray data were collected on an ENRAF-Nonius CAD-4 at 293 K with monochromated Mo K, (A = 0.71073 A radiation) to a 219,, of 23O. A $-scan absorption correction varied from 0.58-1.00. The structure was solved using MULTAN and refined by full-matrix least squares which minimized x w ( W 2 . In the final full-matrix least-squares refinement R = 0.042 for 1346 reflections ( I > 3 4 4 ) and 169 parameters (C and N atoms were refined isotro ically). H atoms were constrained to idealized positions (C-H = 0.95 with isotropic E values of 1.2 times Bcs of the attached C atom. Data collection, structure solution, and refinement parameters are available as supplementary material. Conductivity Measurements. The conductivity measurements were performed with a Keithley 236 unit. Whereas the needle-like a-phase allowed a reliable four-point-probe bar geometry, the platelet samples of the 8-phase were measured with the van der Pauw technique. The resulting error in comparisons between the two phases could be up to a factor of 2 as a result of the geometrical factor. The four contacts were made with gold paint, resulting in a contact resistance that was at least two orders of magnitude higher than the sample resistance. This limited the temperature window of the measurements. The contact resistance decreased on heating the sample, which might be the origin of the scatter in the data points in Figure 6. The carrier density and mobility were
1)
calculated by assuming that the carriers were due to thermal activation across the band (intrinsic semiconductor).' It should be noted that small errors in the determination of the energy gap propagate exponentially in the derivation of the mobility and carrier density. Magnetic Susceptibility Measurements. The magnetic susceptibility was measured from 4.2 to 550 K using the Faraday technique. Details of this apparatus have been previously describedg The applied field was 14 koe,and the measured susceptibility was checked for field dependence at several temperatures. Band Structure Calculations. The band structures were carried out with the EHMACC suite of programs using parameters discussed previously!aJo The off-diagonal elements of the Hamiltonian matrix were calculated with the standard weighting formula."
Acknowledgment. Financial support at Guelph was provided by the N a t u r a l Sciences and Engineering Research Council of Canada and at Arkansas by the National Science Foundation ( E P S C O R program) and the State of Arkansas. Supplementary Material Available: Tables of crystal data, structure solution, and refinement ( S l ) , atomic coordinates (S2), bond lengths and angles (S3), and anisotropic thermal parameters (S3) for &1,3-[(Se2N2C)C6H4(CN2Se2)] (7 pages). Ordering information is given on any current masthead page. (9) (a) DiSalvo, F. J.; Waszczak, J. V. Phys. Reu. 1981, 8 2 3 , 457. (b) DiSalvo, F. J.; Menth, A.; Waszczak, J. V.; Tauc, J. Phys. Rev. 1972, E6, 4574.
(10) Basch, H.; Viste, A.; Gray, H. B. Theor. Chim. Acta 1965, 3, 458. (1 1) Ammeter, J. H.; Burghi, H. B.; Thibeault, J. C.; Hoffmann, R. J . Am. Chem. SOC.1978, 100, 3686.
Redistribution of Reduced Thiophene Ligands in the Conversion of (C,R,)Rh( q4-C4Me4S)to [ (C5R5)Rh13( V4,V '-C4Me4S)2 Shifang Luo, Anton E. Skaugset, Thomas B. Rauchfuss,* and Scott R. Wilson Contribution from the School of Chemical Sciences, University of Illinois, Urbana, Illinois 61801. Received July 8, 1991
Abstract: The thermal decomposition of ( C , M ~ , ) F U I ( ? ~ - C ~ M(1) ~ ~ Shas ) been examined by spectroscopic, kinetic, and structural studies. Compound 1cleanly eliminates free C4Me4Sto give [(CsMeS)Rh],(v4,v1-C4Me4S)2 (2a). The structure of the analogous (2b) conists of a pair of (CSMe4Et)Rh(v4-C4Me4S)ligands bound to a central compound [(CSMe4Et)Rh]3(q4,~1-C4Me4S)2 (CSMe4Et)Rhrunit through the sulfur atoms. The conversion of 1 to 2a occurs via a second-order process (in rhodium) with k(60 "C) = 3.94 X lo4 M-'.s-' which implicates an associative mechanism. Activation parameters are AH* = 20.1 f 0.1 kcal/mol and LW= -13.9 3.1 cal/mol.K. Dynamic 'HN M R studies demonstrate that 2a maintains its structure in solution
*
but that it experiences restricted rotation about the two Rh-S bonds. Compound 2a decomposes via a first-order process with k(100 "C) = 8.94 X 10" s-' to give (CSMe5)2Rh2C4Me4S, 3.
Introduction The chemistry of thiophene-metal interactions has been of recent interest with emphasis on structural and reactivity principle~.~ A large number of thiophene complexes has been prepared in recent years, and several bonding modes have been identified.2 ~~
~~
~
(1) Rauchfuss, T. B. Prog. Inorg. Chem. 1991, 39, 259. Angelici, R. J. Coord. Chem. Reu. 1990,105,61. Angelici, R. J. Acc. Chem. Res. 1988, 21, 387. (2) Some recent studies of thiophene complexes: (a) Ganja, E. A,; Rauchfuss, T. B.; Wilson, S. R. Organometallics 1991, 10, 270. (b) Jones, W.D.;Dong, L. J. Am. Chem. Soc. 1991,113,559. (c) Wang, D.-L.; Hwang, W.-S. J . Organomet. Chem. 1991, 406, C29. (d) Riaz, U.; Curnow, 0.; Curtis, M. D. J. Am. Chem. SOC.1991,113, 1416. (e) Clark, P. D.; Fait, J. F.; Jones, C. G.; Kirk, M. J. Can. J . Chem. 1991, 69, 590. (f) Choi, M.-G.; Robertson, M. J.; Angelici, R. J. J . Am. Chem. SOC.1991, 113, 4005.
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Studies on thiophene complexation have been motivated by intense interest in the molecular mechanisms of the industrially important hydrodesulfurization process (HDS)., In HDS liquid fossil fuels are subjected to catalytic hydrogenation conditions with the goal of cleaving the constituent C-S bonds to give a sulfur-free hydrocarbon. Thiophene derivatives a r e particularly common constituents in fossil fuels4 and a r e of special interest because of (3) Gates, B. C.; Katzer, J. R.; Schuit, G. C. A. Chemisfry of Catalytic Processes; McGraw-Hill: New York, 1979. Zonnevylle, M. C.; Hoffmann, R.; Harris, S. SurJ Sci. 1988, 199, 320. Harris, S.; Chianelli, R. R. J . Catalysis 1986, 98, 17. (4) Geochemistry of Sulfur in Fossil Fuels; Orr, W. L., White, C. M.,
Eds.; American Chemical Society: Washington, DC, 1990. Galperin, G. D. Chemistry of Heterocyclic Compounds; Gronowitz, S., Ed.; John Wiley & Sons, Inc.: New York, 1986; Vol. 44, Part 1, p 325.
0 1992 American Chemical Society
